**Acknowledgements**

We appreciate Prof. Lada Bozic's invitation. Many thanks to Prof. Huai Zhang, Yuanze Zhou, and Guiping Zhao for their kind help in field work. We thank Jiaqi Sun who supplied the pictures of Zibaishan ice cave. This research is supported by the National Natural Science Foundation of China (NSFC), project 41590860 and U1839207.
